Green’s Dictionary of Slang

(Aus./US) to obtain, e,g, a drink or an entrance ticket, without payment.

1887		Daily Trib. (Bismarck, ND) 23 Oct. 4/1: When trying to get trusted for a drink a man is ‘bracing the bar,’ ‘singing a song,’ ‘stifling his jag’ or ‘sparring.’.
1893		St Louis Post-Dispatch (MO) 3 Dec. 17/7: ‘To spar for meals’ means to struggle for life.
1908		Sun. Times (Perth) 1 Mar. 4/8: ’Op inter the Guvvinor Broome ter spar a shicker. [...] I’ve only got a ha’penny, two ’airpins [...] an’ a couple er gelerteen lozengers.
1910		Sun. Times (Perth) 17 Apr. 2nd sect. 9/1: They Say [...] That a lot of Perth Cricket Association members have cause to be ashamed. That they calmly sparred in on their passes to the Pericles Week Carnival.